(a) Field of the Invention
The present invention relates to a nanocomposite blend composition having superior barrier properties, and more particularly to a nanocomposite blend composition having superior mechanical strength and superior barrier properties to oxygen, organic solvent, and moisture, and which is applicable to single/multi-layer blow molding and film processing.
(b) Description of the Related Art
General-purpose resins, such as polyethylene and polypropylene, are used in many fields due to their superior moldability, mechanical properties, and moisture barrier properties. While these resins have good gas barrier properties as well, they are limited in use for packaging or containers for agrochemicals and foods, which require superior oxygen barrier properties. Therefore, packaging or containers (bottles) for such materials are manufactured in multi-layers by co-extrusion, lamination, coating, etc.
Multi-layer plastic products made of an ethylene-vinyl alcohol (EVOH) copolymer and polyamide are transparent and have good gas barrier properties. However, because ethylene-vinyl alcohol and polyamide are more expensive than general-purpose resins, their contents in the products are restricted, and it is required to make the ethylene-vinyl alcohol and polyamide as thin as possible.
To reduce production costs of plastic containers, a method of compounding ethylene-vinyl alcohol and polyamide with inexpensive polyolefin has been proposed. However, because ethylene-vinyl alcohol and polyamide are not very compatible with polyolefin, the blending is not easy. If ethylene-vinyl alcohol and polyamide are blended insufficiently, mechanical properties of produced films or sheets become poor.
In this regard, a method of using a compatibilizer to increase compatibility of ethylene-vinyl alcohol and polyamide to polyolefin has been proposed. Because the compatibilizer increases compatibility of ethylene-vinyl alcohol and polyamide to polyolefin, selection of a good compatibilizer is an important technical issue in improving mechanical strength and chemical barrier properties of products.
U.S. Pat. No. 4,971,864, U.S. Pat. No. 5,356,990, EP No. 15,556, and EP No. 210,725 disclose a method of using a compatibilizer prepared by grafting polyethylene and maleic anhydride. While this compatibilizer increases oxygen barrier properties and mechanical strength, moisture barrier properties are poor due to the hydrophilic properties of ethylene-vinyl alcohol polyamide and ionomers. Therefore, hydrophobic resin processing at the outermost layer is difficult, and there is no suitable processing condition for obtaining effective barrier property morphology.
As disclosed in U.S. Pat. Nos. 4,739,007, 4,618,528, 4,874,728, 4,889,885, 4,810,734, and 5,385,776, a nanocomposite is an exfoliated or intercalated platelet, tactoidal structure, or dispersion mixture thereof of nanometer dimensions, comprising intercalated clay dispersed in a matrix polymer, such as an oligomer, a polymer, or a blend thereof.
In general, nanocomposite manufacturing technology is divided into two methods.
The first method is the manufacturing method of said polyamide nanocomposite. In this method, monomers are inserted within intercalated organic clay, and the clay platelets are dispersed through inter-layer polymerization. This method is restricted in that it is applicable only when cationic polymerization is possible.
The other method is the melt compounding method which inserts melt polymer chains within intercalated clay and exfoliates it through mechanical compounding. Examples of such method are disclosed in Preparation of polystyrene nanocomposite (R. A. Vaia, et. al, Chem. Mater., 5, 1694(1993)), Preparation of polypropylene nanocomposite (M. Kawasumi, et. al, Macromolecules, 30, 6333(1997)), and Preparation of nylon 6 nanocomposite (U.S. Pat. No. 5,385,776), etc.
Therefore, research on nanocomposite blend compositions having superior mechanical strength and chemical barrier properties and that are capable of realizing effective barrier property morphology is needed.